Self-aligned process for nanotube/nanowire FETs

ABSTRACT

A complementary metal oxide semiconductor (CMOS) device, e.g., a field effect transistor (FET), that includes at least one one-dimensional nanostructure that is typically a carbon-based nanomaterial, as the device channel, and a metal carbide contact that is self-aligned with the gate region of the device is described. The present invention also provides a method of fabricating such a CMOS device.

RELATED APPLICATIONS

This application is a continuation application of U.S. Ser. No.12/125,501, filed May 22, 2008, which is a continuation application ofU.S. Ser. No. 11/866,627, filed Oct. 3, 2007, which is a divisionalapplication of U.S. Ser. No. 11/031,168, filed Jan. 7, 2005, now U.S.Pat. No. 7,598,516.

DESCRIPTION Field of the Invention

The present invention relates to a semiconductor structure and a methodof fabricating the same. More particularly, the present inventionrelates to a complementary metal oxide semiconductor (CMOS) device,e.g., a field effect transistor (FET), that comprises at least oneone-dimensional nanostructure that is typically a carbon-basednanomaterial, as the device channel, and a metal carbide contact that isself-aligned with the gate region of the device, i.e., aligned to anedge of the gate region. The present invention also provides a method offabricating such a CMOS device.

BACKGROUND OF THE INVENTION

In the field of molecular nanoelectronics, few materials show as muchpromise as one-dimensional nanostructures, and in particular carbonnanotubes that comprise hollow cylinders of graphite that have adiameter of a few Angstroms. Nanotubes and other like one-dimensionalnanostructures can be implemented in electronic devices, such as, forexample, diodes and transistors, depending on the nanoparticleselectrical characteristics. One-dimensional nanostructures are uniquefor their size, shape, and physical properties. For example,carbon-based nanotubes resemble a hexagonal lattice of carbon rolledinto a cylinder.

Besides exhibiting intriguing quantum behaviors even at roomtemperature, carbon-based nanotubes exhibit at least two importantcharacteristics, a nanotube can be either metallic or semiconductingdepending on its chirality, i.e., conformational geometry. Metallicnanotubes can carry an extremely large current density with constantresistivity. Semiconducting nanotubes can be electrically switched “on”or “off” as field effect transistors (FETs). The two types may becovalently joined (sharing electrons). These characteristics point tonanotubes as excellent materials for making nanometer-sizedsemiconductor circuits. Similar properties exist for otherone-dimensional nanostructures.

Carbon-based nanotubes and other like one-dimensional nanostructures arethus becoming strategically important for post-Si FET scaling. However,there is no known self-aligned process comparable to conventional CMOStechnology. A self-aligned process for a CMOS device includingone-dimensional nanostructures would provide a simpler sequence ofprocessing steps as compared to a non-self-aligned process and itreduces processing error that typically occurs when a non-self-alignedprocess is used. Moreover, a self-aligned process provides a structurehaving reduced parasitics as compared to a non-self-aligned structure.

In view of the above, there is a need for providing a self-alignedprocess for fabricating a CMOS device that includes one-dimensionalnanostructures, such as nanotubes and nanowires.

SUMMARY OF THE INVENTION

The present invention provides a self-aligned one-dimensionalnanostructure-containing field effect transistor (FET) as well as amethod of fabricating the same. The inventive self-alignedone-dimensional nanostructure-containing FET includes a metal carbide asa contact that is aligned to an edge of the gate region that includesthe nanostructures as the device channel.

In the present invention, the term “one-dimensional nanostructure” isused to describe at least one nanotube and/or at least one nanowire.Nanotubes differ from nanowires because nanotubes typically have ahollow cavity, whereas nanowires are completely filled nanomaterials.The term “nanorods” is sometimes used in describing nanowires.One-dimensional nanostructures are structures with nanometer-sizeddiameters and much, much longer lengths. In other words, the structureshave a high aspect ratio and quantum effects become important for thesesystems.

Specifically and in broad terms, the inventive one-dimensionalnanostructure-containing FET comprises:

a substrate comprising at least one gate region located thereon, said atleast one gate region comprising a layer of at least one one-dimensionalnanostructure; and

a metal carbide contact located on a surface of said substrate that isaligned to an edge of said layer of at least one one-dimensionalnanostructure.

In one embodiment of the present invention, the one-dimensionalnanostructure is a nanotube. In another embodiment of the presentinvention, the one-dimensional nanostructure is a nanowire. The at leastone one-dimensional nanostructure used in the present invention istypically a carbon-based nanomaterial that is formed utilizingtechniques well known to those skilled in the art of nanotechnology.

In addition to providing the aforementioned semiconductor structure, thepresent invention also provides a method of fabricating the same. Theinventive method includes the steps of:

providing a structure that includes at least one gate stack on a surfaceof a layer of at least one one-dimensional nanostructure;

forming a source/drain metal on the structure including at least saidlayer of at least one one-dimensional nanostructure; and

forming a metal carbide by reacting said source/drain metal with saidlayer of at least one one-dimensional nanostructure.

In some embodiments of the present invention, the portion of the layerof the at least one one-dimensional nanostructure, not protected by theat least one gate stack, is doped. In such an embodiment, the metalcarbide is formed on the exposed and undoped portion of the layer of atleast one one-dimensional nanostructure.

In another embodiment of the present invention, spacers are formed onthe sidewalls of the at least one gate stack prior to forming the metalcarbide. Spacers are used when a self-aligned silicide anneal process isused. If a non self-aligned silicide anneal is used, the spacers may beomitted.

In another embodiment of the present invention, the at least oneone-dimensional nanostructure is embedded within a conductive compoundthat is generated by the reaction of the source/drain metal with anunderlying substrate that includes C or oxide. The embedding occursduring the carbide annealing step mentioned above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B are pictorial representations (through cross sectionalviews) illustrating various types of initial substrates that can beemployed in the present invention.

FIG. 2 is a pictorial representation (through a cross sectional view)illustrating the initial substrate of FIG. 1A after forming a layer ofat least one one-dimensional nanostructure thereon.

FIG. 3 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 2 after forming a gate dielectric anda patterned gate electrode thereon.

FIG. 4 is a pictorial representation (through a cross sectional view)illustrating a structure similar to that shown in FIG. 3 except that theinitial substrate used is the one illustrated in FIG. 1B and alignmentmarks are utilized. Note that if the gate is much smaller than thecontacts, part of the device could be built out of metallic nanotubesinstead of semiconducting ones.

FIG. 5 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 3 after patterning the gatedielectric.

FIG. 6 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 5 during optional doping of theexposed portion of the layer of at least one one-dimensionalnanostructure.

FIG. 7 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 6 after forming optional first andsecond dielectric layers.

FIG. 8 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 7 after the second dielectric layerhas been selectively etched.

FIG. 9 is a pictorial representation (though a cross sectional view)illustrating the structure of FIG. 8 after the first dielectric layerhas been selectively etched.

FIG. 10 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 9 after performing an optional stepin which a metal compound is formed over the optionally doped portion ofthe layer of at least one one-dimensional nanostructure.

FIG. 11 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 9 after forming a source/drain metallayer thereon.

FIG. 12 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 11 after performing a carbideannealing step.

FIG. 13 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 12 after etching away excesssource/drain metal.

FIG. 14 is a pictorial representation (through a cross sectional view)illustrating a structure similar to that shown in FIG. 13 except thatthe initial substrate shown in FIG. 1B was employed.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, which provides a one-dimensionalnanostructure-containing FET and a method of fabricating the same, willnow be described in greater detail by referring to the drawings thataccompany the present application. The various drawings of the presentinvention are provided for illustrative purposes and thus they are notdrawn to scale. Also, the drawings depict the presence of a single gateregion; the term “gate region” is used herein to denote the gate, gateelectrode and underlying device channel. Although a single gate regionis depicted and described, the present invention also contemplatesforming a plurality of such gate regions and thus a plurality ofone-dimensional nanostructure-containing FETs on a surface of asubstrate.

The present invention begins with first providing the initial substrateshown in either FIG. 1A or FIG. 1B. The initial substrate 10A shown inFIG. 1A comprises a semiconductor layer 12 which includes a dielectriclayer 14 thereon. The semiconductor layer 12 includes any type ofsemiconducting material including, but not limited to: Si, SiGe, SiC,SiGeC, GaAs, InAs, InP or any other III/V or II/VI compoundsemiconductor. The semiconductor layer 12 may also comprise a layeredsemiconductor such as, for example, Si/SiGe or Si/SiGeC. Alternatively,the semiconductor layer 12 may comprise a silicon-on-insulator (SOI) ora silicon germanium-on-insulator (SGOI). The semiconductor layer 12 canbe undoped or doped with one or more doping regions at this point of thepresent invention. Also, the semiconductor layer 12 may be strained orunstrained and it may have any crystallographic orientation including,for example, (111), (110) or (100). Also, the semiconducting substrate12 can be used either for a back gate or for building other devicesnearby (on the same chip or not) with conventional techniques.

In some embodiments of the present invention, when the dielectric layer14 is thick, the semiconductor layer 12 may be replaced with a handlingsubstrate such as a metal or glass. The present invention alsocontemplates embodiments when the entire substrate is comprised of thedielectric layer 14.

The dielectric layer 14 may comprise an oxide, a nitride, an oxynitride,a carbon containing dielectric such as, diamond like carbon (DLC) orfluorinated DLC, a high k dielectric (k greater than 4.0, typicallygreater than 7.0), an organic dielectric or multilayers thereof. In oneembodiment, the dielectric layer 14 comprises an oxide such as SiO₂ or anitride such as Si₃N₄. In another embodiment, the dielectric layer 14comprises a DLC layer.

The dielectric layer 14 shown in FIG. 1A is formed on the surface of thesemiconductor layer 12 utilizing a conventional deposition process suchas, for example, chemical vapor deposition (CVD), plasma-enhancedchemical vapor deposition (PECVD), chemical solution deposition,sputtering, atomic layer deposition (ALD), physical vapor deposition(PVP), spin-on coating, epitaxial growth and other like depositionprocessing. In an alternate embodiment of the present invention, thedielectric layer 14 can also be formed by thermal oxidation, nitridationor oxynitridation.

The thickness of the dielectric layer 14 formed atop the semiconductorlayer 12 may vary depending on the type of dielectric material employedas well as the technique that was used to form the same. Typically, thedielectric layer 14 has a thickness from about a fraction of a nanometerto about 500 nm, with a thickness from about 1 to about 10 nm being moretypical. The aforementioned ranges are for semiconductor substrates andfor back gate processes. For substrates without electricalfunctionality, the whole substrate can be a dielectric or the dielectricthickness can be extremely thick.

FIG. 1B shows another substrate 10B that can be used in the presentinvention. Specifically, the initial substrate 10B shown in FIG. 1Bincludes a semiconductor layer 12, a dielectric layer 14, and regions ofa C-containing compound 16 embedded within the dielectric layer 14. TheC-containing compound 16 can be any compound material that includes Csuch as, for example, DLC, or fluorinated DLC. The C-containing compound16 is formed by blanket depositing the dielectric layer 14 on thesurface of the semiconductor layer 12, forming a patterned photoresist(not shown) on the surface of the dielectric layer 14 and etching anopening into the dielectric layer 14 which defines the area for theembedded C-containing compound 16. The patterned photoresist is formedby conventional processing including applying a photoresist to thesurface of the dielectric layer 14, exposing the photoresist to apattern of radiation and developing the exposed photoresist utilizing aconventional resist developer. The etching step, which forms an openinginto the dielectric layer 14, includes a dry etching process such asreactive-ion etching, ion beam etching, plasma etching or laserablation. In addition to dry etching, the present invention alsocontemplates using a wet etch to provide the openings for forming theembedded regions within the dielectric layer 14.

With the patterned mask in place, the C-containing compound 16 isdeposited forming the structure shown, for example, in FIG. 1B. Thedepth of the C-containing compound 16 formed into the dielectric layer14, as measured from the upper surface of the dielectric layer 14, isfrom about 1 nm to about 500 nm or more, with a depth from about 5 toabout 20 nm being more typical.

Unless otherwise specified, the description that follows utilizes theinitial substrate 10A. Although initial substrate 10A is specificallyutilized, the present invention and the following processing steps workequally well for the alternative initial substrate 10B shown in FIG. 1Bor with a non-semiconducting substrate.

Next, and as shown in FIG. 2, a layer of at least one one-dimensionalnanostructure 18 is formed atop the dielectric layer 14; in the case inwhich initial substrate 10B is utilized, the layer of at least oneone-dimensional nanostructure 18 is formed atop the surfaces of both thedielectric layer 14 and the embedded C-containing compound 16.

The layer of at least one one-dimensional nanostructure 18 may include ananotube, a nanowire or a combination of these two types ofnanomaterials. As stated above, nanotubes differ from nanowires becausenanotubes typically have a hollow cavity, whereas nanowires arecompletely filled nanomaterials. One-dimensional nanostructures arestructures with nanometer-sized diameters and much, much longer lengths.In other words, the structures have a high aspect ratio and quantumeffects become important for these systems.

In one highly preferred embodiment of the present invention, the layerof at least one one-dimensional nanostructure 18 comprises nanotubes,while in another highly preferred embodiment of the present inventionthe layer of at least one one-dimensional nanostructure 18 comprisesnanowires.

The nanotubes that can be used in the present invention are singlewalled or multi-walled nanomaterials that have an outer diameter that istypically from about 0.4 nm to about 30 nm, with an outer diameter fromabout 0.8 nm to about 2.5 nm being more typical, and a length that istypically from about 5 nm to about 100 μm, with a length from about 10nm to about 10 μm being more typical. In addition to having an outerdiameter, the nanotubes that can be used in the present invention havean inner diameter that is typically from about 0.4 nm to about 15 nm,with an inner diameter from about 0.8 nm to about 2.5 nm being morehighly typical. The nanotubes useful in the present invention arefurther characterized as having a high aspect ratio that is typically onthe order of about 5 or greater, with an aspect ratio from about 5 toabout 5000 being more typical.

The nanowires that can be used in the present invention comprise variousatomic layers, i.e., more than one shell, in which the outer diameter istypically from about 0.4 nm to about 100 nm, with an outer diameter fromabout 0.8 nm to about 50 nm being more typical, and a length that isfrom about 5 nm to about 100 μm, with a length from about 10 nm to about10 μm being more typical. The nanowires useful in the present inventionare further characterized as having a high aspect ratio that istypically on the order of about 5 or greater, with an aspect ratio fromabout 5 to about 5000 being more typical.

The layer of at least one one-dimensional nanostructure 18 employed inthe present invention typically includes a C-based nanomaterial that hasa hexagonal lattice structure that is rolled up. That is, thenanostructures of the present invention typically are comprised ofcarbon, e.g., graphite. Although C-based nanomaterials are preferablyused, the present invention also contemplates other types ofnanomaterials such as metallic or a combination of C-based and metallic.

The thickness of the layer of at least one one-dimensional nanostructure18 formed at this point of the present invention can vary depending onthe technique that was used to form the same. Typically, the layer of atleast one one-dimensional nanostructure 18 has a thickness from about0.4 to about 500 nm, with a thickness from about 0.8 to about 50 nmbeing more typical. In embodiments in which nanotubes are used, thelayer of nanotubes 18 typically has a thickness from about 0.8 to about3 nm.

The term “layer of at least one one-dimensional nanostructure” is usedherein to denote a layer that includes at least one nanotube or nanowireas well a layer that contains a controlled and selected number of suchone-dimensional nanostructures. Preferably, layer 18 includes aplurality of one-dimensional nanostructures thus the remaining text usesthe phrase “layer of one-dimensional nanostructures”.

The layer of one-dimensional nanostructures 18 can be formed utilizingtechniques that are well known in the art. For example, carbon-basednanotubes can be produced by arc-discharge and laser ablation of acarbon target. Alternatively, carbon-based nanotubes can be made bychemical vapor deposition in the presence of metallic particles.Specific process details for nanotube formation that can be used in thepresent invention can be found, for example, in S. Iijima, et al.“Helical Microtubes of Graphite Carbon”, Nature 354, 56 (19991); D. S.Bethune, et al. “Cobalt Catalyzed Growth of Carbon Nanotubes withSingle-Atomic-Layer Walls” Nature 363, 605 (1993), and R. Saito, et al.“Physical Properties of Carbon Nanotubes”, Imperial College Press(1998); the entire content of each is incorporated herein by reference.Also, the catalyst-free growth method disclosed in co-assigned U.S.Patent Application No. 2004/0035355 A1 can be used in fabricatingnanotubes that can be used as layer 18. The entire content of the '355published application is also incorporated herein by reference. In oneembodiment of the present invention, the layer of carbon nanotubes 18 isformed by chemical vapor deposition at 900° C. for 10 min using Fecatalyst particles.

Carbon-based nanowires can also be produced by arc-discharge and laserablation of a carbon target. Alternatively, carbon-based nanowires canbe made by chemical vapor deposition in the presence of metallicparticles. Specific process details for nanowire formation that can beused in the present invention can be found, for example, in S. Botti, etal., Chemical Physics Letters vol. 355, no. 5-6: 395-9, 8 Apr. 2002; theentire content of which is incorporated herein by reference. In oneembodiment of the present invention, the layer of carbon nanowires 18 isformed utilizing laser-induced chemical vapor deposited amorphoushydrogenated carbon nanoparticles (from a mixture of ethylene andacetylene) as precursor (see, for example, S. Botti, et al, J. Appl.Phys. 88, 3396 (2000)), and depositing them onto a heated surface usingthe following conditions: a pressure of about 0.04 atmospheres, asubstrate temperature of about 1100° C., a deposition time of about 90min in an Ar carrier at a flow of about 300 sccm.

Despite illustrating the above techniques for forming the layer of onedimensional nanostructures 18, the present invention also contemplatesother techniques that are capable of forming such nanostructures. Forexample, solution-phase decomposition, sol-gel electrophoresis, orwet-chemical, hydrothermal synthesis can be used in formingone-dimensional nanostructures.

After forming the layer of one-dimensional nanostructures 18 on thesurface of one of the initial substrates shown in FIG. 1A or 1B, a gatedielectric 20 is formed on the surface of layer 18; See FIG. 3. Inembodiments in which the at least one one-dimensional nanostructure isformed directly within a semiconductor substrate, the gate dielectric 20can be formed by a thermal growing process such as, for example,oxidation, nitridation or oxynitridation. Alternatively, the gatedielectric 20 can be formed by a deposition process such as, forexample, chemical vapor deposition (CVD), plasma-assisted CVD, atomiclayer deposition (ALD), evaporation, reactive sputtering, chemicalsolution deposition or other like deposition processes. The gatedielectric 20 may also be formed utilizing any combination of the aboveprocesses.

The gate dielectric 20 is comprised of an insulating material including,but not limited to: an oxide, nitride, oxynitride and/or silicateincluding metal silicates and nitrided metal silicates. In oneembodiment, it is preferred that the gate dielectric 20 is comprised ofan oxide such as, for example, SiO₂, HfO₂, ZrO₂, Al₂O₃, TiO₂, La₂O₃,SrTiO₃, LaAlO₃ or mixtures thereof.

The physical thickness of the gate dielectric 20 may vary, buttypically, the gate dielectric 20 has a thickness from about 0.5 toabout 100 nm, with a thickness from about 0.5 to about 10 nm being moretypical.

After forming the gate dielectric 20, a blanket layer of a gateelectrode 22 is formed on the gate dielectric 20 utilizing a knowndeposition process such as, for example, physical vapor deposition, CVDor evaporation. The thickness, i.e., height, of the gate electrode 22deposited at this point of the present invention may vary depending onthe deposition process employed. Typically, the gate electrode 22 has avertical thickness from about 5 to about 180 nm, with a thickness fromabout 5 to about 50 nm being more typical.

The gate electrode 22 can comprise any conductive material that istypically employed as a gate of a CMOS structure. Illustrative examplesof such conductive materials that can be employed as the gate electrode22 include, but are not limited to: polysilicon, conductive metals,conductive metal alloys, conductive silicides, conductive nitrides,polySiGe or combinations thereof, including multilayers thereof. In someembodiments (not shown), a gate cap comprised of an oxide or nitride canbe formed atop the gate electrode 22. Also, it is possible to form abarrier layer between multiple layers of gate electrode materials.

The blanket layer of gate electrode 22 is then patterned providing thestructure shown in FIG. 3. Patterning of the blanket layer of gateelectrode 22 can be achieved utilizing conventional techniques that arewell known in the art. For example, patterning of the gate electrode 22can be performed by lithography and etching. The lithographic stepincludes applying a photoresist (not shown) to the upper surface of thegate electrode 22 (or optional gate cap, if present), exposing thephotoresist to a desired pattern of radiation and developing the exposedphotoresist utilizing a conventional resist developer. The pattern inthe photoresist is then transferred to the blanket layer of gateelectrode 22 (or optional gate cap first and then gate electrode 22)utilizing one or more etching steps. The etching includes a dry etchingprocess, such as reactive ion etching, ion beam etching, plasma etchingor laser ablation. Wet etching can also be used to pattern the gateelectrode 22. As shown, the etching step selectively etches portions ofthe gate electrode 22, stopping atop the gate dielectric 20. Thepatterned photoresist is typically removed after the pattern has beentransferred into the gate dielectric 20 utilizing a conventionalstripping process. The dimensions of the gate formed can vary from about3 nm to several micrometers, preferably between 7 nm and 1 μm.

FIG. 4 illustrates a structure similar to that shown in FIG. 3 exceptthat the initial substrate used is the one illustrated in FIG. 1B andalignment marks 100 and/or 101 are utilized. The alignment mark 100 isformed into the substrate, while the alignment mark 101 is formed atopthe surface of the gate dielectric 20. The alignments marks 100 and 101are formed utilizing a conventional process well known in the art andthey serve to align the gate level to the underlying substrate.

FIG. 5 shows the structure after the exposed regions of gate dielectric20, not including the patterned gate electrode 22 (and gate cap, ifpresent), are removed. The removal of the exposed portion of the gatedielectric 20 is performed utilizing an etching process that selectivelyremoves gate dielectric material as compared with a gate conductorand/or the layer of one-dimensional nanostructures 18. Dry etching orwet etching is contemplated herein for selectively removing the exposedportions of the gate dielectric 20. As illustrated, this removal stepsexposes a portion of the layer 18 that is adjacent to the gate stack 24.Gate stack 24 includes at least the patterned gate electrode 22 and thepatterned gate dielectric 20. Although a single gate stack 24 is shown,a plurality of such gate stacks can be formed as described above.

Next, and as shown in FIG. 6, the exposed portion of layer 18 is thenoptionally doped with a first conductivity type dopant 26 (either n-typeor p-type) to provide an optional dopant region 28. It is emphasizedthat the doping of the exposed portion of layer 18 is optional and isnot used in all instances. The doping can be performed by electrostaticdoping, gas phase doping or other like doping techniques. Ionimplantation can be used if the layer of one-dimensional nanostructures18 includes nanowires. The dopant 26 can be an n-type dopant whichincludes at least one element from Group VA of the Periodic Table ofElements, or the dopant 26 can be a p-type dopant that includes at leastone element from Group IIIA of the Periodic Table of Elements. Thedoping provides dopant region 28 which typically has a dopingconcentration from about 10¹⁹ to about 10²² atoms/cm³. More typically,the dopant region 28, which is located in the exposed portion of layer18, has a dopant concentration from about 10²¹ to about 10²² atoms/cm³.

Next, and as shown in FIG. 7, dielectric stack 29 comprising one or moredielectric layers is optionally formed. It is noted that the dielectricstack 29 is used to provide spacers on the sidewalls of the gate stack24. In some embodiments where a self-aligned anneal is used, spacerformation is required. In yet other embodiments where a non self-alignedanneal is used, spacer formation is not required.

In some embodiments of the present invention, the dopant implantationstep can occur prior to formation of the spacers or after formation ofone of the spacers and after formation of the other spacer.

In the embodiment illustrated, dielectric stack 29 includes a firstdielectric layer 30 and a second dielectric layer 32. The dielectricstack 29 comprises a dielectric material such as, for example, an oxide,nitride, or oxynitride. A conventional deposition process such asdescribed for the formation of the gate dielectric 20 can be employed informing the dielectric stack 29. Alternatively, the dielectric stack 29is formed by a thermal process. The thickness of the dielectric stack 29may vary, but typically the overall thickness of the dielectric stack 29is from about 5 to about 100 nm.

In some embodiments, the dielectric stack 29 and subsequent spacerformation can occur prior to the optional doping step mentioned above.

In FIG. 7, the dielectric stack 29 includes a first dielectric (i.e.,inner spacer material) 30 and a second dielectric (i.e., outer spacermaterial) 32 which are composed of different dielectric materials. Inone embodiment, first dielectric 30 is comprised of a nitride such assilicon nitride and second dielectric 32 is comprised of an oxide suchas silicon dioxide.

Etching is then performed to remove the dielectric stack 29 from allhorizontal surfaces that were previously covered during deposition. Theetching is shown in FIGS. 8 and 9. Specifically, dry etching, wetetching or a combination thereof is used. As shown in the specificembodiment, a first etch is used to selectively remove the seconddielectric 32 from horizontal surfaces of the structures (See FIG. 8),and then a second etch is used to remove the first dielectric 30 fromhorizontal surfaces of the structure. The resultant structure includinginner spacer 30′ and outer spacer 32′ is shown in FIG. 9. Although dualspacers are shown, the present invention contemplates a single spacer ormultiple spacers located on the sidewall of the gate stack 24.

In an optional embodiment of the present invention, such as shown inFIG. 10, a layer of metal compound 34 is formed atop the dopant region28 that was previously formed into the layer of one-dimensionalnanostructures 18. When employed, the layer of metal compound 34 canalso be formed atop the exposed and undoped portion of layer 18. Thelayer of the metal compound 34 functionalizes the dopant region 28 (oralternatively the exposed and undoped portion of layer 18) and aids inthe formation of metal carbide regions. The layer of the metal compound34 comprises, for example, c-C₄H₆═Mo═O (where c stands for cyclic) suchas described in H. Oudghiri-Hassani et al, “Passivation of metal carbidesurfaces: relevance to carbon nanotube-metal interconnections”, AppliedSurface Science, 212-213, p 4-9 (2003) where the double bond between theorganic group and the conducting carbide can be useful in 1) molecularelectronics applications; 2) some molybdenum alkylidene compounds areactive for metathesis family of reaction to grow covalently graftedpolymeric layers for passivation or manipulation of metal carbidecontacts (see, for example, K. J. Ivin et al, Olefin Metathesis andMetathesis Polymerization, Academic Press, San Diego, 1997; A. Furstneret al, Angew. Chem. Int. Ed. Engl. 39 3012 (2000)).

The layer of metal compound 34 can be deposited selectively such that itreacts chemically with the layer of one-dimensional nanostructures. Whena selective deposition is employed, the layer 34 can go underneath thesidewalls if undercutting occurs (this occurs in instances in which anon-directional etch is used). In some embodiments, a mask level (formedby reactive-ion etching or liftoff) is used during the deposition oflayer 34 such that the layer 34 does not extend beneath the sidewalls.The thickness of the layer of the metal compound 34 may vary dependingon the complex used as well as the technique that was used to form thesame.

Next, a source/drain metal 36 is formed at least atop the exposed dopantregion 28 that was previously formed into portions of layer 18 as shownin FIG. 11. In another embodiment, source/drain metal 36 is formed atleast atop the layer of metal compound 34 shown in FIG. 10. In yetanother embodiment of the present invention, the source/drain metal 36is formed on at least exposed and undoped portions of layer 18.Source/drain metal 36 is formed in the present invention utilizing aconformal deposition process, such as, for example, CVD, PECVD, chemicalsolution deposition, ALD, sputtering, plating, evaporation or other likeprocesses. In one embodiment of the present invention, the source/drainmetal 36 is deposited from a carbon-containing target/source. In onepreferred embodiment of the present invention, the source/drain metal 36is deposited by ALD to increase the current injection areas from metalto nanostructure. In particular, ALD provides a method to provide auniform coverage of source/drain metal 36 around the circumference ofeach nanostructure. That is, a sleeve of the source/drain metal 36 canbe formed around each of the nanostructures within layer 18.

The source/drain metal 36 comprises any metal or metal-like element thatcan react with carbon to form a stable binary metal carbide phase.Alternatively, the source/drain metal may include C and optionally otherelements. Examples of such source/drain metals include: Al, Si, Sc, Ti,V, Cr, Mn, Fe, Y, Zr, Nb, Mo, Hf, Ta, W and mixtures or alloys thereof.Preferably, at least one of Al, Ti, Cr, Mo, W, Zr, Hf or Ta is used asthe source/drain metal 36. The compound formation can be performed indifferent atmospheres such as, for example, nitrogen, forming gas,chloride, bromide, fluoride, oxygen and others. The variation of ambientgases allows for the formation of different conductive compounds eithercontaining the C from the nanotube or embedding the nanotube itself.

The thickness of the source/drain metal 36 may vary depending on themetal used as well as the technique that was used to form the same.Typically, the thickness of layer 36 is from about 3 to about 200 nm,with a thickness from about 5 to about 20 nm being more typical.

After forming the source/drain metal 36 on the structure, the structurecontaining the same is then subjected to an annealing step that isperformed under conditions that cause reaction of the source/drain metal36 with dopant region 28 containing the nanostructures. The resultantstructure that is formed after the anneal has been performed is shown inFIG. 12. As shown, a metal-carbide region 38 forms adjacent to the gatestack 24; the metal-carbide region 38 is aligned to an edge of the gatestack 24 as well as an edge of the remaining layer of one-dimensionalnanostructures 18. The remaining layer of one-dimensional nanostructuresserves as the device channel. Note that the annealing step may leavesome of the source/drain metal 36 on the structure.

In another embodiment (not shown), the anneal causes a reaction betweenthe source/drain metal 36 and an exposed and undoped portion of layer18. This embodiment would also produce a metal-carbide region. In yetanother embodiment, the anneal causes a reaction between thesource/drain metal 36, optionally the layer of metal compound 34 anddoped or undoped portions of layer 18. In still another embodiment ofthe present invention, the anneal step causes embedding ofone-dimensional nanostructures in a conducting compound region that isgenerated by reaction of metal and the underlying substrate including Cor oxide. When embedding occurs, the spacer needs to be comprised of anitride so that the etch selectivity is not lost.

The annealing step used at this point of the present invention to causemetal carbide 38 formation is performed at a temperature of about 600°C. or greater. Typically, the metal-carbide formation anneal isperformed at a temperature from about 750° to about 1100° C. Themetal-carbide formation anneal is performed in an inert ambient such asHe, Ar, Ne, Kr, Xe, N₂ or mixtures thereof such as He—Ar. The anneal isperformed for a time period of sub-milliseconds or greater, with anannealing time from about 10 sec to about 30 min being more typical. Thevery short time anneal are achieved using laser annealing. The annealingcan be performed utilizing a single annealing temperature or multipleannealing temperatures can be used. The annealing may also includevarious ramp-up cycles, soak cycles, and cool down cycles, as desired.

After forming the metal-carbide region 38, the remaining source/drainmetal 36 is removed from the structure utilizing an etching process thatselectively removes metal as compared with metal carbide. FIG. 13 showsone possible structure that can be formed utilizing the above processingsteps. FIG. 14 shows another possible structure that can be formed; FIG.14 differs from FIG. 13 in terms of the type of initial substrate used.In both instances, a semiconductor structure is illustrated thatincludes a substrate 10A or 10B comprises at least one gate regionlocated thereon. The at least one gate region comprises a patterned gatestack as well as the remaining layer of one-dimensional nanostructures18. A metal carbide contact, i.e., region 38, is located on a surface ofthe substrate and it is aligned to an edge of the least one gate regionas well as the remaining layer of one-dimensional nanostructures 18.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood byone skilled in the art that the foregoing and other changes in forms anddetails may be made without departing from the spirit and scope of theinvention. It is therefore intended that the present invention is notlimited to the exact forms and details described and illustrated, butfalls within the spirit and scope of the appended claims.

What is claimed is:
 1. A method of fabricating a semiconductor structurecomprising: providing at least one gate region on a surface of asubstrate, said at least one gate region comprising a layer of at leastone one-dimensional nanostructure, a gate dielectric located on asurface of said at least one one-dimensional nanostructure and a gateelectrode located on a surface of said gate dielectric, where said layerof at least one one-dimensional nanostructure is interposed between saidsubstrate and said gate electrode; forming at least one spacer on asurface of said layer of at least one one-dimensional nanostructure,wherein an inner edge of said at least one spacer is laterally abuttingboth a sidewall of said gate electrode and a sidewall of said gatedielectric; and forming a metal carbide contact located on a surface ofsaid substrate, wherein said metal carbide contact is aligned to andlaterally abuts, but does not overlap, both a sidewall edge of saidlayer of at least one one-dimensional nanostructure and a sidewall edgeof said at least one spacer.
 2. The method of claim 1 wherein said layerof at least one one-dimensional nanostructure comprises at least onenanotube, at least one nanowire, or a combination of at least onenanotube and at least one nanowire.
 3. The method of claim 1 whereinsaid layer of at least one one-dimensional nanostructure comprises aC-based nanomaterial.
 4. The method of claim 1 wherein said layer of atleast one one-dimensional nanostructure is formed by arc-discharge,laser ablation of a carbon target, or chemical vapor deposition.
 5. Themethod of claim 1 wherein said substrate includes a semiconductor layerand a dielectric layer that has a least one region of a C-containingcompound embedded therein located atop the semiconductor layer.
 6. Themethod of claim 1 further comprising doping a portion of said layer ofat least one one-dimensional nanostructure not protected by at leastsaid gate electrode, said doping comprises electrostatic doping, ionimplantation, or gas phase doping.
 7. The method of claim 1 wherein saidforming the metal carbide contact comprises forming a source/drain metalatop exposed portions of the layer of at least one one-dimensionalnanostructure, and annealing.
 8. The method of claim 7 furthercomprising forming a layer of metal compound atop the exposed portionsof the layer of at least one one-dimensional nanostructure prior toforming the source/drain metal.
 9. The method of claim 7 wherein saidforming said source/drain metal comprises selecting at least one of Al,Si, Sc, Ti, V, Cr, Mn, Fe, Y, Zr, Nb, Mo, Hf, Ta and W and depositingthe same.
 10. The method of claim 9 wherein said depositing comprises anatomic layer deposition process or deposition from a carbon-containingtarget.
 11. A method of fabricating a semiconductor structurecomprising: providing at least one gate region on a surface of asubstrate, said at least one gate region comprising a layer of at leastone one-dimensional nanostructure, a gate dielectric located on asurface of said at least one one-dimensional nanostructure and a gateelectrode located on a surface of said gate dielectric, where said layerof at least one one-dimensional nanostructure is interposed between saidsubstrate and said gate electrode; forming at least one spacer on asurface of said layer of at least one one-dimensional nanostructure,wherein an inner edge of said at least one spacer is laterally abuttingboth a sidewall of said gate electrode and a sidewall of said gatedielectric; and forming a metal carbide contact on a surface of saidsubstrate, wherein said metal carbide contact is aligned to andlaterally abuts, but does not overlap, both a sidewall edge of saidlayer of at least one one-dimensional nanostructure and a sidewall edgeof said at least one spacer, and wherein said at least one spacer doesnot overlap said metal carbide contact.
 12. The method of claim 11wherein said layer of at least one one-dimensional nanostructurecomprises at least one nanotube, at least one nanowire, or a combinationof at least one nanotube and at least one nanowire.
 13. The method ofclaim 11 wherein said layer of at least one one-dimensionalnanostructure comprises a C-based nanomaterial.
 14. The method of claim11 wherein said layer of at least one one-dimensional nanostructure isformed by arc-discharge, laser ablation of a carbon target, or chemicalvapor deposition.
 15. The method of claim 11 wherein said substrateincludes a semiconductor layer and a dielectric layer that has a leastone region of a C-containing compound embedded therein located atop thesemiconductor layer.
 16. The method of claim 11 further comprisingdoping a portion of said layer of at least one one-dimensionalnanostructure not protected by at least said gate electrode, said dopingcomprises electrostatic doping, ion implantation, or gas phase doping.17. The method of claim 11 wherein said forming the metal carbidecontact comprises forming a source/drain metal atop exposed portions ofthe layer of at least one one-dimensional nanostructure, and annealing.18. The method of claim 17 further comprising forming a layer of metalcompound atop the exposed portions of the layer of at least oneone-dimensional nanostructure prior to forming the source/drain metal.19. The method of claim 17 wherein said forming said source/drain metalcomprises selecting at least one of Al, Si, Sc, Ti, V, Cr, Mn, Fe, Y,Zr, Nb, Mo, Hf, Ta and W and depositing the same.
 20. The method ofclaim 19 wherein said depositing comprises an atomic layer depositionprocess or deposition from a carbon-containing target.